Technical Field
[0001] The present invention relates to an ion implantation apparatus and an ion implantation
method used in fabrication processes of semiconductor devices.
Background Art
[0002] For semiconductor devices typified by VLSI circuits, there are constant desires for
much higher integration density and higher performance. In order to meet such desires,
it is necessary to carry out the fabrication processes of semiconductor devices under
optimal conditions. For this reason, the optimal conditions of each fabrication process
were found out heretofore by preliminarily producing trial semiconductor devices under
various conditions and evaluating characteristics of the trial semiconductor devices
thus produced.
[0003] In the case of ion implantation processes among the semiconductor fabrication processes,
it was ordinary practice to preliminarily carry out ion implantation under various
conditions in order to find optimal conditions. Of course, since the ion implantation
is carried out with ion implantation apparatus, the conditions of ion implantation
substantially mean operation conditions of the ion implantation apparatus.
[0004] The ion implantation apparatus is basically comprised of an ion beam generator for
generating ions and selecting desired ion species to form an ion beam thereof, and
an ion implantation section for directing the ion beam from the ion beam generator
toward a silicon wafer for process to implement ion implantation. A well-known ion
implantation section is of a type consisting of a target chamber the interior of which
is kept in vacuum, and a wafer support wheel located in this target chamber. The wafer
support wheel consists of a swing shaft mounted in a swingable state in the target
chamber, a hub mounted in a rotatable state at a distal end of the swing shaft, and
a plurality of arms radially extending from the hub, each arm having a wafer holder
for holding a silicon wafer at the distal end thereof. The wafer support wheel is
arranged to rotate around the hub and swing in a plane perpendicular to the ion beam
so that the entire surface of wafer is irradiated with the ion beam.
Disclosure of the Invention
[0005] The conventional ion implantation apparatus as described above is operated so as
to uniformly implant the ions over the entire wafer surface in a single ion implantation
process. In other words, doses of a wafer processed by the conventional, ordinary
ion implantation apparatus are almost uniform in the wafer surface. For this reason,
for example, in order to evaluate a plurality of ion implantation conditions, it was
necessary to prepare and process wafers in the number equal to at least the number
of conditions.
[0006] However, all chips obtained from one wafer were not necessary for determining the
conditions of ion implantation by evaluating device characteristics. Therefore, many
chips were wasted. Particularly, as the size of wafers has been increasing in recent
years, more chips have been wasted and the cost per wafer has been becoming higher.
Accordingly, there arises the problem in the method of uniformly implanting the ions
over the entire wafer surface.
[0007] In order to evaluate a plurality of ion implantation conditions by use of a single
wafer, there was also a conventional idea of forming plural types of different dose
areas on a single wafer. This method, however, required masking or the like, so as
to increase the number of steps for ion implantation, thus increasing the cost.
[0008] An object of the present invention is to provide an ion implantation apparatus and
an ion implantation method capable of forming plural types of dose areas on a single
wafer by a single ion implantation process, without the need for masking or the like.
[0009] In order to accomplish the above object, an ion implantation apparatus according
to the present invention comprises an ion beam generator for generating an ion beam;
a wafer support wheel for supporting a wafer to be implanted, the wafer support wheel
being rotatable for revolution of the wafer so that the ion beam from the ion beam
generator scans an entire surface of the wafer; a first drive motor for rotating the
wafer support wheel; a swing shaft for supporting the wafer support wheel; a second
drive motor for swinging the swing shaft and the wafer support wheel, the second drive
motor being able to be driven in forward and backward directions and being adjustable
in velocity; and control means for controlling swing velocity of the wafer support
wheel by rotating the second drive motor, based on either of a plurality of basic
swing velocity modes preset so as to uniformly implant ions in the entire surface
of the wafer, wherein the control means controls the second drive motor so that either
one basic swing velocity mode out of the plurality of basic swing velocity modes is
switched to another basic swing velocity mode at a switch position arbitrarily selected
in a swing range of the wafer support wheel.
[0010] The present invention of the above construction was invented based on the idea that
the swing velocity of the wafer support wheel was able to be instantaneously and suddenly
changed by using the motor capable of being driven in both forward and backward directions
and adjustable in velocity, as the second drive motor for swinging the wafer support
wheel. Thanks to the provision of the control means as described above, a certain
basic swing velocity mode is switched to another basic swing velocity mode in the
middle of the swinging operation of the wafer support wheel in the swing range, so
as to instantaneously change the swing velocity of the wafer support wheel, whereby
several different dose areas are formed on the wafer as a result. Consequently, plural
types of dose areas can be formed with accuracy on a single wafer by a single ion
implantation process, without the need for masking or the like.
[0011] In the ion implantation apparatus of the present invention, more specifically, the
control means is preferably one comprising setting means for setting a control swing
velocity mode in which either one basic swing velocity mode out of the plurality of
basic swing velocity modes is switched to another basic swing velocity mode at the
switch position selected, and drive control means for rotationally driving the second
drive motor according to the control swing velocity mode set by the setting means.
[0012] In order to accomplish the above object, an ion implantation method of the present
invention is a method using an ion implantation apparatus comprising an ion beam generator
for generating an ion beam; a wafer support wheel for supporting a wafer to be implanted,
the wafer support wheel being rotatable for revolution of the wafer so that the ion
beam from the ion beam generator scans an entire surface of the wafer; a first drive
motor for rotating the wafer support wheel; a swing shaft for supporting the wafer
support wheel; and a second drive motor for swinging the wafer support wheel and the
swing shaft according to a basic swing velocity mode preset so as to uniformly implant
ions in the entire surface of the wafer, the second drive motor being able to be driven
in forward and backward directions and being adjustable in velocity, wherein during
ion implantation, the second drive motor is driven so that a basic swing velocity
mode is switched to another basic swing velocity mode of a different dose at a switch
position arbitrarily selected in a swing range of the wafer support wheel.
[0013] This permits plural types of dose areas to be formed on a single wafer by a single
ion implantation process, without the need for masking or the like, as described above.
Brief Description of the Drawings
[0014]
Fig. 1 is an exploded perspective view of an ion implantation apparatus according
to the present invention.
Fig. 2 is a block diagram to show a control system for operating a wafer support wheel
illustrated in Fig. 1.
Fig. 3 is an example of a control swing velocity mode stored in a memory of a control
unit illustrated in Fig. 2.
Best Mode for Carrying Out the Invention
[0015] A preferred embodiment of the present invention will be described below with reference
to the drawings.
[0016] Fig. 1 is an exploded perspective view to show an embodiment of the ion implantation
apparatus according to the present invention. The ion implantation apparatus 10 is
provided with an ion beam generator 12 for generating an ion beam, an ion implantation
section 14 for implanting the ion beam from the ion beam generator 12 in silicon wafers
W for process, and a wafer loader section 16 for supplying silicon wafers W into the
ion implantation section 14.
[0017] The ion beam generator 12 consists of well-known elements including an ion source
system, an ion beam extraction preacceleration system, a mass analyser system, a postacceleration
system, and so on, which are not illustrated. The ion source system is arranged to
induce discharge of doping gas supplied from a gas supply source (not illustrated)
to create a high density plasma state. The ion beam extraction preacceleration system
extracts and accelerates ions constituting the above plasma by making use of a potential
difference from the ion source system, thereby forming an ion beam. The mass analyser
system selects only desired ion species out of the ion beam and the postacceleration
system accelerates the beam of the desired ion species toward the ion implantation
section 14.
[0018] The ion implantation section 14 is provided with a target chamber 18 of a box type
the interior of which is kept in vacuum, and a wafer support wheel 20 disposed in
the target chamber 18. An opening 22 is bored in one wall surface of the target chamber
18 and the ion beam from the ion beam generator 12 emerges through this opening 22.
A beam stop 24 (see Fig. 2) is provided at a position opposite to the opening 22 in
another wall surface of the target chamber 18. The beam stop 24 is a member for receiving
the ion beam having passed the wafer support wheel 20.
[0019] The wafer support wheel 20 consists of a swing shaft 26 mounted in a swingable state
in the target chamber 18, a hub 28 mounted in a rotatable state at the distal end
of this swing shaft 26, and a plurality of arms 30 radially extending from the hub
28. A wafer holder 32 for supporting a wafer W is provided at the distal end of each
arm 30. The hub 28 rotates in a direction of an arrow A and the swing shaft 26 swings
in a predetermined swing angle range along directions of arrows B. As a result, the
wafers W supported on the respective wafer holders 32 each cross the ion beam from
the ion beam generator 12, so that the ion beam irradiates the entire surface of each
wafer, thereby implementing ion implantation.
[0020] Fig. 2 is a block diagram to show a control system for actuating the wafer support
wheel 20. The ion implantation system 10 is provided, in addition to the aforementioned
configuration, with a first drive motor 34 for rotating the hub 28 in the direction
of the arrow A, a second drive motor 36 for swinging the swing shaft 26 along the
directions of the arrows B, a rotation sensor 38 for detecting swing angles of the
swing shaft 26, an input device 40 for selecting and entering either one mode out
of a plurality of control swing velocity modes described hereinafter, and a control
unit 42 for executing predetermined arithmetic processing based on signals from the
rotation sensor 38 and the input device 40 and controlling the second drive motor
36.
[0021] The first drive motor 34 is attached to a drive arm 44 coupled to the swing shaft
26 and rotates the hub 28 at fixed velocity through a drive transmission mechanism
such as a belt not illustrated. The second drive motor 36 is a motor that is able
to rotate in both forward and backward directions and is adjustable in velocity. The
motor 36 is fixed to a mount bracket not illustrated, and swings the swing shaft 26
and the wafer support wheel 20 through a belt 46.
[0022] The control unit 42 has a memory 42A, a target setting section 42B, an arithmetic
processing section 42C, and an amplifying section 42D.
[0023] The memory 42A is a storage unit for preliminarily storing a plurality of control
swing velocity modes specifying velocity variations for the swing shaft 26 to swing
between the two end positions. The swing velocity herein means velocity of the rotational
center of the wafer support wheel 20. The control swing velocity modes will be described
below in detail.
[0024] Fig. 3 shows one of the plurality of control swing velocity modes stored in the memory
42A. In Fig. 3 the X-axis represents the swing angle θ of the swing shaft 26 relative
to one end position of the swing shaft 26 and the Y-axis the swing velocity v of the
swing shaft 26. In the same figure θ1 indicates a swing angle of the swing shaft 26
at the time when the wafer support wheel 20 is located at an implant position where
the ions are implanted in a portion of the wafer W most distant from the center of
the hub 28 (which will be referred to hereinafter as "first position"), and θ2 is
a swing angle of the swing shaft 26 at the time when the wafer support wheel 20 is
located at an implant position where the ions are implanted in a portion of the wafer
W nearest to the center of the hub 28 (which will be referred to hereinafter as "second
position"). The positive domain of the Y-axis (the upper region with respect to the
X-axis) indicates velocities at which the second drive motor 36 rotates to swing the
swing shaft 26 from the first position to the second position, and the negative domain
of the Y-axis (the lower region with respect to the X-axis) velocities at which the
second drive motor 36 rotates in the reverse direction to swing the swing shaft 26
from the second position to the first position.
[0025] In Fig. 3, the solid line P with arrows represents a control swing velocity mode,
and this control swing velocity mode P is comprised of a combination of two basic
swing velocity modes Q and R. Here the basic swing velocity modes are modes to specify
preset swing velocities of the swing shaft 26 so that the ions are uniformly implanted
in the wafer W, i.e., so that doses of the wafer W become uniform, with swinging of
the swing shaft 26 between the two end positions. In the basic swing velocity mode
Q indicated by the dashed line, the swing velocities v of the swing shaft 26 are represented
by v = f(θ) + C1. On the other hand, the swing velocities v of the swing shaft 26
in the basic swing velocity mode R indicated by the chain line are represented by
v = f(θ)/2 + C2, and thus are approximately half of the swing velocities v in the
basic swing velocity mode Q throughout the entire range of the swing angles θ of the
swing shaft 26. For this reason, doses of the wafer W with swinging of the swing shaft
26 according to the basic swing velocity mode Q are approximately half of doses of
the wafer W with swinging of the swing shaft 26 according to the basic swing velocity
mode R.
[0026] During the swinging motion of the swing shaft 26 from the first position to the second
position according to the control swing velocity mode P as described above, the swing
velocities first vary according to the basic swing velocity mode Q and then the swing
velocities vary according to the basic swing velocity mode R after arrival at the
intermediate position (hereinafter referred to as "switch position") between the first
position and the second position. In the swinging motion of the swing shaft 26 from
the second position to the first position according to the control swing velocity
mode P, the swing velocities first vary according to the basic swing velocity mode
R and then the swing velocities vary according to the basic swing velocity mode Q
after arrival at the switch position.
[0027] Now returning to Fig. 2, the target setting section 42B reads a control swing velocity
mode selected and entered at the input device 40, out of the memory 42A and sets it
as a target of feedback control. The arithmetic processing section 42C accepts a value
detected by the rotation sensor 38, calculates an actual swing velocity of the swing
shaft 26 from this detected value and an internal timer (not illustrated), and compares
this actual swing velocity with the target swing velocity set at the target setting
section 42B to find a command value to control the actual swing velocity to the target
swing velocity. The amplifying section 42D amplifies the command value obtained at
the arithmetic processing section 42C to generate a control signal, and sends this
control signal to the second drive motor 36.
[0028] In the above configuration the plurality of control swing velocity modes each comprised
of a combination of two basic swing velocity modes are preliminarily stored in the
memory 42A, but a plurality of basic swing velocity modes may be stored in the memory
42A. In this case, the apparatus is constructed so that the input device 40 selects
and enters two basic swing velocity modes out of the plurality of basic swing velocity
modes, the target setting section 42B reads the two basic swing velocity modes selected
and entered, out of the memory 42A, and these modes are combined to generate a control
swing velocity mode.
[0029] In the control unit 42 as described above, the memory 42A and the target setting
section 42B constitute setting means for setting a control swing velocity mode in
which either one basic swing velocity mode out of the plurality of basic swing velocity
modes is switched to another basic swing velocity mode at the switch position selected,
and the arithmetic processing section 42C and the amplifying section 42D do drive
control means for rotationally driving the second drive motor 36 according to the
control swing velocity mode set by the setting means.
[0030] With the ion implantation apparatus 10 of the present embodiment of the above structure,
for example, when ion implantation is implemented in trial production and evaluation
of semiconductor devices, the robot (not illustrated) carries a plurality of wafers
W accommodated in a cassette (not illustrated) in the wafer loader section 16, into
the target chamber 18 and mounts the wafers on the respective wafer holders 32 of
the wafer support wheel 20. While the wafer support wheel 20 is then rotated in the
direction of the arrow A by the first drive motor 34, the wafer support wheel 20 is
swung from the first position to the second position along the direction of the arrow
B by the second drive motor 36, whereby the ion beam from the ion beam generator 12
impinges upon the entire surface of each wafer W to implant it.
[0031] Supposing at this time the control swing velocity mode P as illustrated in Fig. 3
is selected and entered out of the plurality of control swing velocity modes at the
input device 40, the wafer support wheel 20 first swings at the velocities according
to the basic swing velocity mode Q, then the wafer support wheel 20 instantaneously
lowers its velocity upon arrival at the intermediate switch position between the first
position and the second position, and thereafter the wafer support wheel 20 swings
at the velocities according to the basic swing velocity mode R. Accordingly, two dose
regions of approximately equal areas corresponding to the basic swing velocity modes
Q and R are formed in each wafer W. A dose in a half region is double a dose in the
other half region in the surface of each wafer W.
[0032] Since the present embodiment permits two different dose areas to be formed in a single
wafer W by a single ion implantation process as described above, it can obviate the
need for masking or the like and decrease the number of steps thereby, thus decreasing
the time and cost necessary for the ion implantation. Since a single ion implantation
process yields chips with different characteristics from a single wafer, the number
of waste chips can also be reduced, and thus the cost can also be reduced in this
respect.
[0033] The present embodiment is the example wherein the swing velocities of the wafer support
wheel 20 are controlled according to the control swing velocity mode comprised of
the combination of two basic swing velocity modes to form two different dose areas
in a single wafer W, but the present invention does not have to be limited particularly
to this embodiment; for example, the apparatus may also be arranged in such manner
that the swing velocities of the wafer support wheel 20 are controlled according to
a control swing velocity mode comprised of a combination of three or more basic swing
velocity modes to generate three or more different dose areas in a single wafer W.
[0034] The present invention can also be applied to actual fabrication of semiconductor
devices, as well as the trial production and evaluation of semiconductor devices.
Industrial Applicability
[0035] Since the present invention permits plural kinds of dose areas to be formed on a
single wafer by a single ion implantation process without the need for masking or
the like, it can increase efficiency and decrease cost. Since a plurality of chips
with different characteristics are yielded from one wafer by a single ion implantation
process, the number of waste chips can also be reduced and the cost can also be decreased
in this respect.
1. An ion implantation apparatus comprising:
an ion beam generator for generating an ion beam;
a wafer support wheel for supporting a wafer to be implanted, said wafer support wheel
being rotatable for revolution of said wafer so that the ion beam from said ion beam
generator scans an entire surface of said wafer;
a first drive motor for rotating said wafer support wheel;
a swing shaft for supporting said wafer support wheel;
a second drive motor for swinging said swing shaft and said wafer support wheel, said
second drive motor being able to be driven in forward and backward directions and
being adjustable in velocity; and
control means for controlling swing velocity of said wafer support wheel by rotating
said second drive motor, based on either one of a plurality of basic swing velocity
modes preset so as to uniformly implant ions in the entire surface of said wafer,
wherein said control means controls said second drive motor so that either one basic
swing velocity mode out of said plurality of basic swing velocity modes is switched
to another basic swing velocity mode at a switch position arbitrarily selected in
a swing range of said wafer support wheel.
2. The ion implantation apparatus according to Claim 1, wherein said control means comprises:
setting means for setting a control swing velocity mode in which either one basic
swing velocity mode out of said plurality of basic swing velocity modes is switched
to another basic swing velocity mode at said switch position selected; and
drive control means for rotationally driving said second drive motor according to
the control swing velocity mode set at said setting means.
3. An ion implantation method using an ion implantation apparatus, said ion implantation
apparatus comprising an ion beam generator for generating an ion beam; a wafer support
wheel for supporting a wafer to be implanted, said wafer support wheel being rotatable
for revolution of said wafer so that the ion beam from said ion beam generator scans
an entire surface of said wafer; a first drive motor for driving said wafer support
wheel; a swing shaft for supporting said wafer support wheel; and a second drive motor
for swinging said wafer support wheel and swing shaft according to a basic swing velocity
mode preset so as to uniformly implant ions in the entire surface of said wafer, said
second drive motor being able to be driven in forward and backward directions and
being adjustable in velocity,
wherein during ion implantation, said second drive motor is driven so that a basic
swing velocity mode is switched to another basic swing velocity mode of a different
dose at a switch position arbitrarily selected in a swing range of said wafer support
wheel.